Compressor or pump



Nqv. 9, 1948.

w. BELL QOMPRESS OR OR PUMP 1O Sheets-Sheet 1 Filed Oct. 19, 1944 INVENTOR. Harvey W Bel/ BY ,wawww ATTORNEYS Nov.9,1948; H, w, B 2,453,402

COMPRESSOR OR PUMP Filed Oct. 19, 1944 I l0 Sheets-Sheet 2 .J F/QZ. m

. INVENTOR. Harvey 14/ Bell z waww ATTO/f NE Y5 Nov. 9, 1948. H. w. BELL 2,453,402

COMPRESSOR OR PUMP Filed Oct. 19, 1944 1o Sheets-Sheet 3 IN VEN TOR.

R H'ar vey W Bell i ATTORNEYS H. w. BELL- COMPRESSOR OR PUMP Nov. 9, 1948.

10 Sheets- Sheet Filed Oct. 19, 1944 INVENTOR. Har vey W fie/l ATTORNEYS Nov. 9, 1948. H. w. BELL COMPRESSOR OR PUMP Filed Oc t; 19, 1944 1Q Sheets-Sheet 5 ATTORNEYS H. w. BELL COMPRESSOR OR PUMP 1o sheets-sheet 6 Filed Oct. 19, 1944 I V mmvrom Harvey WBe/l BY v . ATTORNEYS MQWW Nov. 9, 1948. H. \UN.BEL L v 2,453,402

COMPRESSOR OR PUMP Filed Oct. .19, 1944 I losheets-rsheet 7 INVENTOR. Harvey W Bell NOV. 9, 1948. W, BELL 2,453,402

I COMPRESSOR 0R PUMP Filed Oct. 19', 1944 10 Sheets-Sheet a 2 H463 92%.. I Q /07 H INVENTOR. Harvey W Bell ATTORNDS N"ov.9,194s. B L 2,453,402

' COMPRESSOR OR PUMP Filed Oct. 19, 1944 l0 Sheets-Sheet 9 INVENTOR. Harvey W Bell A TTORNEYS Nov. 9, 1948. v

H. w. BELL 2,453,402

COMPRESSOR 0R PUMP Filed Oct. 19, 1944 10 Sheets-Sheet l0 INVENTOR. Harvey W fiel/ A T TORNEYJ Patented Nov. 9, 1948 FFICEL 2,453,402 COMPRESSOR on PUMP Harvey W. Bell, Yonkers, N. y. Application October 19, 1944, "Serial No. 559,361

pending application "Serial No. 497,781, now

abandoned, or is intended to serve as a power amplifying torque converter. In such compressors, if variations in Volumetric displacement are to be accomplished by means 'of an unloading valve operable to render ineffective a selected portion of thecompression stroke, then the clearance space in the compressor presents aproblem. If this unloading valve is prematurely opened during the initial stages of the suction stroke, the air compressed in the clearance space during the compression stroke is released through said valve during the suction'stroke, so that a portion of the work of compression will be lost. This clearance loss increases as the pressure ratio is increased.

It is also important that'for any one final pressure, the ratios of effective displacements of the different cylinders in a multi-stage compressor be maintained substantially constant with changes in these effective displacements, and that the ratio be such as to substantially equalize the work and heat generated in the cylinders. For example, if the compressor is two-stage and is designed to compress air to a final pressure of 220 lbs. gage at sea level, then the displacement of the low pressure cylinder should be about four times that of the high pressure cylinder, or the ratio of compression in each cylinder should be about four, This ratio of compression in each cylinder and the ratio of displacements of the two cylinders should be maintained with variations in the output of the compressor.

One object of the present invention is to provide a compressor having new and improved means for varying its effective displacement or capacity.

Another object is to provide a compressor havingncomparatively simple but, nevertheless, effective means for varying by infinite increments its effective displacement. i

.A further object is to provide a .multi-stage compressor having :means for varying the effec- (Cl. 2s0-21) 'tive displacement of the cylinders of its different stages simultaneously.

Another object is to provide new and improved compressor features which vary the effective displacement or capacity of the compressor, and which may beemployed to vary the output of a single or multi-stage compressor.

Another object is to provide new and improved compressor features which vary the effective displacement or capacity of a compressor, and which are operable for manual or automatic control. l

Another object is to provide new and improved compressor features which vary the effective displacement or capacity of a compressor, and which may be employed to maintain automatically a nearly constant pressure in a receiver or storage tank of a system in which the demand for compressed air varies, without varying the speed of the compressor or subjecting it to shock as a result of a sudden change in the load.

A further object is to provide new and improved means which vary the effective displacement or capacity of a compressor, and which maybe employed to equaliae the work of compression of the different stages of a multi-stage compressor for different final pressures. In carrying out this ob'jectof the invention, the cylinders of a multistage compressor may be correctly proportioned for one final pressure, and the compressor may be efliciently employed for a greater or lesser final pressure by adjusting the mechanism to proportion correctly the eifective displacements of the-different cylinders of the different stages for the new final pressure. The same multistage compressor maybe efficiently employed for i the same or a different gage pressure at different altitudes by adjustment of the control of the effective displacements of the different cylinders of the different stages for equalization. of the work of the stages.

Another-object is to provide new and improved means which vary the effective displacement or capacity of a compressor, and which may be employed in connection with a prime mover, such as an internal combustion engine, to compress and deliver air in infinitely variablerati-os of volume and pressure. In carrying out this object of the presentinvention, the power of the engine may-be employed to compress and deliver air at-a relatively high pressure, but in relatively small volumes, or may be employed to compress and deliver a greater volume of air at alower-pressure,

Ihis feature makes possible a pneumatic torque converter somewhat as the variable stroke hydraulic pump makes possible the hydraulic torque converter. With this feature, the power of the prime mover may be employed to supply a relatively large volume of relatively low pressure air to an air motor to drive it at high speed when the torque requirement is low, or the power of the prime mover may be employed to supply air at a relatively high pressure, but in small volumes, to drive an air motor when the torque requirement is high.

A further object is to provide new and improved compressor features which vary the effective displacement or capacity of a compressor, and which are arranged to permit rotation of the crankshaft of a compressor in either direction without its effective displacement being altered for any adjustment of its control memher.

In accordance with certain features of the present invention, the cylinder of the compressor, whether it is of the single stage or multi-stage type, has an unloading valve which is positively maintained by a mechanical device in open position from the beginning of the compression stroke to a selected phase of said stroke prior to the opening of the discharge or delivery valve. As far as certain aspects of the present invention are concerned, this unloading valve may be the only inlet suction valve of the cylinder, or may be provided in addition to the ordinary inlet valve. While this unloading valve is open, air cannot be compressed in the cylinder and compression cannot begin until this valve is closed. This valve is initially opened during the final stages of the suction stroke, and is maintained open during the initial stages of the compression stroke, according to the setting of the valve control means. Means are provided for adjusting the phasing of the opening and closing of the unloading valve with respect to the stroke cycle of the piston. This adjustment is desirably so effected that the point in the suction stroke when the valve opens (as measured from the end of the suction stroke) corresponds to the phase in the compression stroke when said valve closes (as measured from the beginning of the compression stroke). For example, when the compressor is running with its displacement 100% effective, there is no mechanical opening or closing of the unloading valve; at 50% displacement, it would be opened approximately at midsection of the suction stroke if suction has not previously opened it and closed at midsection of the compression stroke; at onethird capacity, the unloading valve is opened during the suction stroke after the piston has travelled approximately one-third of said stroke, and is closed after traveling two-thirds of its compression stroke; and at zero displacement, it is open throughout the Whole of the suction and compression strokes.

The unloading valve is so operated that, with any adjustment of its control, it remains closed during the suction stroke until the pressure of the air in the cylinder is less than the pressure of the air in the inlet pipe. Therefore, at the end of the compression stroke, any compressed air in the clearance space will be reexpanded against the piston, and will not be released through the unloading valve. The work of compressing this air in the clearance space is thereby returned to the piston and will not be lost.

As a further feature, in one of the embodiments of the invention, the means for varying the displacement of the compressor cylinder is automatically operated to maintain the pressure at the delivery end of the compressor or in a receiver substantially constant, at any desired pressure.

As another feature of the present invention, the mechanical means for operating the unloading valves in the different cylinders of a multistage compressor are interconnected and adjusted from a single control in such a manner that the effective displacements of the cylinders of the different stages are varied alike so that the ratio of compression of the different stages is not varied with different compressor outputs, provided the final pressure remains the same.

Due to the fact that under certain conditions some of the air which is taken into the cylinders is discharged therefrom before compression starts, efiective internal cooling of the cylinder and valves is obtained.

Various other objects, features and advantages of the invention will be apparent from the following particular description, and from an inspection of the accompanying drawings, in which:

Fig. l is a vertical section of a two-stage singleacting compressor taken on the line l-I of Fig. 6 through the low pressure cylinder, and embodying certain features of the present invention;

Fig. 2 is a vertical section of the compressor taken axially through the high pressure cylinder on the line 2-2 of Fig. 6;

Fig, 3 is a horizontal section of the compressor taken on line 3-3 of Fig. 2;

Fig. 4 is a vertical section of the compressor taken on line 4-4 of Fig. 2, and showing the working portion of said compressor;

Fig. 5 is a section of the control means for varying the effective displacement of the compressor cylinders taken on line 4-4 of Fig. 2, and constituting a continuation at the right hand end of Fig. 4;

v Fig. 6 is a horizontal section of the compressor taken along line 6-6 of Fig. l, and showing the workingparts of the compressor;

Fig. 7 is a top plan view of part of the compressor, and constituting a continuation of Fig. 6 at the right hand end thereof;

Fig. 8 is a side elevation of the cam and follower device for controlling the effective displacement of the low pressure cylinder;

Figs. 9, 10, 11, 12, 13 and 14-. are sections taken along the lines 99, ifllll, ll- I l, l2--I2, |3-l3 and i l-14 respectively of Fig. 8;

Fig. 15 is a top plan view somewhat diagrammatic showing a general arrangement of a twost-age compressor with its intercooler and pipe connections 2 Fig. 16 is a top plan view of a multi-cylinder two stage compressor of the present invention provided with a single intercooler;

Fig. 1'7 is a top plan view somewhat diagrammatic showing a 'multicylinder two-stage compressor oi the present invention having a common outlet, but having more than one intercooler, and

Fig. 18 is a vertical section, somewhat diagrammatic showing the present invention embodied in a double acting compressor.

The present invention is shown in Figs. 1-15 for the purpose of illustration, embodied in a twostage single-acting compressor ID in which the low pressure cylinder H and the high pressure cylinder [2 are vertically arranged in line. The

air or other gas to be compressed is compressed :to a certain pressure in the low pressure cylinder ll, passes to an intercooler l3 (Fig. 15) in which its temperature is reduced, and finally enters the ensaaoc casting 'l'fih'as the nec essary bores-to define the; two adjoining: cylinders I I and I 2. The head end or the low pressure cylinder II is provided 'withs-a removable head I! constituting a water 'ia'eket (Fig. 1) having'aninlet I8 and an-outlet "2U ior th'e circulating coo1lng'water. The high pressurecylinder :I2 is similarly provided with a head 2I also'in the form of a jack-et'(Fig. 2) with inlet and outlet connections ZZ and'23 for the circulating water. Radiating ribs 24 on the two cylinders I I and I2 serve to abstract further the heat of compressionir'om the air.

Reciprocable in the low pressure cylinder II is a pistondfl 'pivotally attached in the usual man- 'ner -to -one end of a connecting rod 28, the other end 'b'eing pivotallysecured to a crank 30, ai'zfixed toa crank shaft 3I journ-aled in split bearings 3 Ia in-thecrankcase I6, arid'in bearings 3| b of end plates 3lc secured to the opposite ends of the casing i 6. The high pressure cylinder I2 is similarly provided with apiston 32 driven in the usual manner "from the crankshaft 3| by means of a crank 33 on said crank shaft, and a connecting rod 34 between said crank and said piston. Clou-nter weights 35 and 36 on the cranks 30 and "3'3,'a-ndta flywheelfll (Fig. 4) .on the crank shaft .3! serve their usual counterbalancing and speed equalizing "function.

Th8 tWO cranks '30 and 33 are shown 180 apart on the-crank shaft 3!, so thatwhile one piston is undergoing its suction stroke, the other piston is traveling in -the direction of its compression stroke.

,The'driving power'for the crank shaft'SI is derivedifrom an suit-able source, such as a steam engine or electric or gas motor which may be connected to one end of the crank shaft 3 I. i

:The air-or other gas fromthe atmosphere or other source, passesthrough a filter 40 and into the inletport H. of the lowpressure cylinder II (FigsfBfi and 15). This inlet port 4| leads into one side-"of the workingendof thelow pressure cylinder II opposite'to and-nearthe lower end of its 'hea'dnor Water jacket I1, and iscontrolled by aninletvalve 42 ofanywell known construction. :Thistinlet Valve 42 is showngior the purpose of i1- iustration, or: the usual thin-plate type.

Leading'irom one side of the working end of the low .pressurecylinder II alongside head I! near its lowerrend is a discharge port (Fig. 3) connected to the inlet of the intercooler I3 through a pipei l-ll (see Fig. 15 also) andcuntrolled by a discharge valve 45, shownfor the purposes -ofillustration of the usual thin-plate type. This discharge port 43 I is circumferentially spaced about 90ifromthe inlet port 13 I.

'fIhe twovalves142 and'45 each have a plurality ofts'pringsfpressing against the valve'plate so as to 'be automatically operablein accordance with thepressure in the cylinder I I. During the downwardsucti-on stroke of the piston '27, the inlet valveciz is automatically opened to permit the inhuction of air by suction therein, and during the hpwardicompress-ion stroke, the inlet valve 42 is olosedz' by the pressure of the :air in the cylinder IL -and hyritsrsp-rings and when said pressure slightly exceeds the pressure in the outletpipe, thervalve 45 is/automat'ically openedagainst the action' of Jits spring or springs. I -'-The "compres'se'd 6 air is thereupon discharged; fr-omrthe ccylin'deriitt, through the pipe 44 'andzinto"thesinletofathe inter'cooler 1J3. I

The .air J-fr-om the outlet of the .interc'ooler II3 is delivered by a pipe- 41, :seeagain Figs. 3 and L15, to an inlet port 5480f the high pressure cylinder I2. This inlet :port 48 communicates with rantinlet "valve 50 and an unloading valve flz to? be :described. :Anloutlet valve 52Lin 'dischargeaportifiii is located opposite unloading va1ve '82 :in 'cylinder l2 The operation 'ofLt-he high pressure 'stalge of the compressor is similar to that described in connection .withthe low'pressure stage. :Ihe discharge Ivalve 52 permits the passage of the air through a pipe-52a into areceiver 53 from :which it may be conducted, through a valve controlled pipetttohe used as desired.

As :a feature of the present'linvention, means are pro'vid'edfor controlling the effective displacements 1 of the two: cylinders in the propertproportions tormaintain the ratios ofthese displacements substantially equal. The means :for controlling the effective displacement of the low pressure cylinder II comprises an unloading port 55 (Figs. 3 and .15) inthe side of said cylinder diametrically opposite the r discharge porti4'3, and communicating with the inlet port '41 through an 'arcuate passageway- 55 extending around said cylinder. An unloading valve 5I in the port 55 and shownof the-poppet mushroom typje, comprises a conical disc da adapted to cooperate with a conical valvese'at 6t in-the wall of thecylinder II. Rigid with the -valvedisc 58 is a stem fil supported for axial movement in a: slide hearing 62 forming part of la valvehousing I 63. This bearing 62 has a fiange 64 'iforming one waiver the housing -63, and secured to the easting *15 bystuds SE. The depending section ofthis flange 64 may be provided with a series =of racliating ribs 66. Forming the other part of the valve housing'63 andconnected to the flange 64 and to the-c'asting I5 bythe studs fi5 is-a housing section 61.

The valve 5'! is normally maintained inthe closed position shown in Fig. 3 'bymeans of a coil spring :68 in the housing :63 encircling the valve -stem fil, -and'bearing-at one end against the fixed bearing filand atthe other end against an abutment collar '10 affixedto the outer end of said .valvestem.

The" valve 511s maintained in open-position by means of a rocker arm "I I disposed in the housin'g 63 and secured-at one end to a rocker shaft "l2 j0urnaled in the housing section fi'l. The other endof the rocker arm II is arranged to maintain the valve-5'! positively opened, andfor that purpose has a tappet 13 adapted to'engage the outerenidof the valve stem==6 I Theihighpressure cylinder IZis similarly pro -vi ded with an unloading port disposed substantially diametrically opposite I the discharge p0rt 5I ofsa-id cylinder, and communicating with theeinlet port 48 through an arcuatepassageway III. A springeclosed unloadingvalve 82 similar to'Ithe' valve 51 and similarly disposed in a housing 19 c0ntr01sthe flow through the port BIl, and is-positively. maintained in open position by means of a5 rocker arm -83 afiixed to -a 'ro'cker shaft 84 journaled in a valve housing section 85.

*Theunloading valve 5'! of the low pressure cylinder II is positively operated by a cam (Figs. 1, 6 an'd 8) :in the former aI-shaft journalediati its ends in thetrcrankcase LI 6, and provided 'withzitapering cam conformations ontaperingdwell to be described. This cam 90 is rotated at the same angular speed as the crank shaft 3| through a sprocket chain drive 9|. In follower engagement with the periphery of the cam 90 is a roller 92 supported for rotation between a pair of lever arms 94 rigid with and extending substantially radially from a hub 95 splined to a shaft 96 for slidable movement therealong, and keyed to said shaft for rotation therewith. This shaft 96 is journaled in the crankcase I6.

As the cam 90 rotates, the follower roller 92 moves substantially vertically (Fig. 1), causing corresponding angular oscillatory movement of the lever arms 94, and a corresponding rotary movement of the shaft 96. The rocking movements of the shaft 96 are transmitted to the rocker shaft I2 by means of a lever arm 91 (Figs. 1 and 3) affixed to one end of the rocker shaft .12 outside the valve housing 63, and having at its free end a ball and socket connection 98 with one end of a link I00. The other end of this link I has a ball and socket connection I 0| with the outer end of a lever arm I02 aflixed outside the crankcase I6 to the shaft 96 for angular oscillation therewith.

A spring I03 in the housing 5?, bearing at its ends against a radial extension of the rocker arm II and against a wall of said housing, serves to maintain the roller 92 constantly in follower engagement with the cam 90.

The cam 90, as shown in Figs. 8 and 14, has a cylindrical section I05 near one end, a cylindrical section I06 of smaller diameter near the other end, and an intermediate section I01 having a radial cam projection or dwell I08 merging into said end sections and progressively widening at its radially outer end along a circular arc I09 coextensive with the periphery of the larger cylindrical end section I95 as said projection approaches said larger end section. The roller 92 and the cam 90 are moved relatively axially, as described hereinafter to move said roller 92 to any selected portion of said cam according to the desired effective displacement of the cylinder II.

As the radially outer forward side of the cam projection or dwell I08 rides underneath the follower roller 92 during the suction stroke of the piston 21, it opens the unloading valve 51, and as the rear side of said cam projection I08 passes underneath said roller, the valve 5'! under the action of its spring 68 is closed. The opening and closing phases of the valve 5'! relative to the cycle of the piston 2! depends on the width of the cam projection or dwell I08 at its radially outer end in the plane of the follower roller 92, and this in turn depends on the axial position of said roller with respectto the cam 90.

The unloading valve82 of the high pressure cylinder I2 is controlled by a'cam II5 journaled in the crankcase I6, and extends parallel to the cam 90, Figs. 1, 2, 4 and 6. This unloading valve 82 is disposed on the side of the vertical plane of the common center line of the two cylinders II and I2 opposite tothe unloading valve 51 of the low pressure cylinder II, so that the cam M5 for operating said valve 82 is disposed on the same side, and on the side of the crank shaft 3| opposite to the cam 90. This cam H5 is rotated at the same angular speed as the crank shaft 3| by means of a sprocket chain drive H6, and operates the valve 82 in a manner similar to that already described in connection with the operation of the valve 51. This operation is effected through a cam roller II I supported on and between a pair of lever arms IIB rigidly extending from a hub I20, which is splined to a shaft I2I for rotation therewith, and for axial movement therealong. This shaft I2I is journaled in the crankcase I6, and rigidly carries near one end outside said crankcase a crank arm I22 operating a lever arm I23 through a link I24 having ball and socket end connections with said arms. The lever arm I23 is affixed to one end of the rock shaft 04 on the outside of the valve housing I9, so that the up and down cam follower movement of the roller II! is translated into oscillatory angular movement of said rocker shaft 83, and in turn into opening and closing movements of the escape valve 82.

The rocker shafts 72' and 84 project outside their respective housings 63 and 19in opposite directions and towards opposite ends of the crankcase I6 in position to receive their transmissions from the shafts 96 and I2I to the unloading valves BT and 82. The projecting parts of these rocker shafts I2 and 84 are supported in bearings I25 and I26 respectively rigid with respective housing sections 61 and 85. To prevent leakage of air through the bearing I26 associated with the high pressure cylinder it is provided with a stuiiing box I26a (Fig. 3) in the end nearest the arm I23 and the opposite end of said bearing is closed.

The two cams and H5 are similar in construction, and have similar cross-sections at common transverse planes, but since the two cranks 30 and 33 are 180 apart onv the crank shaft 3], said cams are also disposed, 180 apart, so that while the valve opening projection on one cam extends upwardly, the corresponding projection on the other cam extends downwardly as shown in Fig. 1. With this arrangement of the two cams 90 and I I5, it is possible to rotate the crank shaft 3| in either direction without the effective displacements of the cylinders being altered with any adjustment of the control lever I50 to be described.

For moving the follower rollers 92 and I I1 along their respective cams 90 and H5, there is provided a pair of parallel guide rods I30-and I3I (Figs. 1 and 4 to '7), fixed at one end at I32 and I33 respectively to an end wall of the crankcase I6, and extending through the opposite end wall of said crankcase and to a control device I34 to be described. At the other end, these guide rods I30 and I3I are secured to the respective posts I35 and I36 extending up from and secured to the base I61). Embracing the guide rods I30 and I3I with a slidable fit are a pair of long sleeves I 37 and I38 respectively extending throughan end wall of the crankcase I6, and terminating at its outer end near the control device I34. At the inner end in the crankcase, the sleeve I31 has rigid therewith fork I40 having arcuate fingers extending into a circumferential groove MI in the periphery of the hub supporting the cam roller 92. in the crankcase I6 with a fork I42 having arouate fingers extending into a circumferential groove I43 in the periphery of the hub I20 supporting the cam roller In. With thisconstruction, the movement of the sleeves I3! and I38 axially along their respective guide rods I30 and I3I causes movement of the cam rollers 92 and I I! along their respective cams 90 and H5 without interfering with radial oscillatory movement of the hubs 95 and I20. y 1

The sleeves I31 and I38 are axially moved in unison along their guide rods I30 and, IN. and

The sleeve I38 is similarly provided ae aeoz into selected position with respect to their respective cams 9n and Us by means of the control device I34. This control device. I34 which is one form of the invention comprises a bracket frame I44 secured to the base I61) and having opposed stanchions I45 and I 46. Rigid with the upper end of one of the stanchions I 45 is. a sector I41 provided with a series of notches I48 to assist in holding. the cam rollers 92 and H1 in their adjusted positions according to effective displacement desired by the cylinders. An upstanding lever control handle I 50 is secured at its lower end to a rocker shaft II which is supported by the frame stanchions I and I46. A sleeve I52, supported on that portion of shaft I 5| located between the stanchions I46 and I41,

has two parallel arms I53 and I54. This sleeve I52 is secured to the shaft I5I and its arms I53 and I54 are disposed in the longitudinal plane of the control handle I (Fig. 5). The arms I53 and I54 have link connections at their lower ends with the slide sleeves I31 and I38 respectively. The link connections for the arm I53 includes a link I55 pivotally connected at its ends with the lower end of the arm I53 and the slide sleeve I31, and the link connection with the arm I54 includes a link I55 pivotally connected atits ends with the lower endoi the arm I54 and the slide sleeve I38.

The control handle I50 is held in any selected I position with respect to the notched periphery of the sector I41 so as to maintain the cam rollers 92 and H1 in their adjusted positions. This locking of the handle I50 is done by means of a detent I which is slidable in a bearing IBI alnxed to said handle, and which is normally pressed into handle locking position in any selected notch I 48 by a coil spring I52. The detent I60 and notches I48 are so formed that the handle I50 can readily be moved into any selected position by the detent riding over the teeth and dropping into any one of the notches. This angular movement of the control handle I50 causes angular movement of the two parallel arms I53 and corresponding endwise movement of the two slide sleeves I31 and I38 along their guide rods I 30 and I 3| This movement of the slide sleeves I31 and I38 is transmitted to the roller supporting sleeves or hubs 95 and I20, so that the follower. rollers 92 and H1 are moved along their respective cams 00 and H5, and in selected position with respect thereto, as determined by the position of the control handle I50.

The compressor cylinders II and I2 are designed for the particular final pressure against which the compressor is intended to do most of its work. Assuming that the compressor is intended to operate normally against a final pressure of 220 lbs. gage at sea level, then the displacement of the low pressure cylinder II should be about fOLlI times that of the high pressure cylinder I2. Assuming that the pistons 21 and 32 have the same stroke, the relative capacities of the two stages would vary as the square of the diameters of the cylinders, the

diameter of the low pressure cylinder I I- would be about twice that of the high pressure cylinder I2, toaiford a four to one displacement ratio between the two cylinders II and I2. In the presentinvention the high pressure cylinder is made of. slightly larger diameter thanabove stated but the displacement ratio of 4 to l is maintained by giving the high pressure piston 32 a shorter stroke than. that of the low pressure cylinder. With the dimensional. proportions disclosed, the

10 low pressure cylinder II will. compress the air from atmospheric at sea level to. about44.3 lbs. gage, which corresponds to a ratio of compression of four, and the second cylinder will compress the air from 44.3 to 220 lbs. gage, which also corresponds to a ratio of. compression of, four.

If it is desired, for example, to operate the compressor at. 100% capacity, the control handle I50 is set to bring the follower rollers 92 and 1 into the position shown in Fig. 14, in which said rollers engage the smaller cylindrical end sections of said cams respectively. In this position, the cam rollers 92 and H1 will be in their lowermost position, and will remain there during the operation of the compressor, so that the unloading valves 51 and 82 will remain closed during the entire operating cycle unless opened by suction. When the control handle I50 is set to position the follower rollers 92 and M1 on the intermediate sections of the respective cams 00 and H5 carrying the radial valve opening projections, the valves 51 and 82 will be positively held open during a selected phase of the suction stroke of the piston and a portion of the compression stroke thereof.

' The cam then permits the closing of the unloading Valve for the remainder of the compression stroke of the piston. If, for example, it, is desired to pump to the same pressure but only one-third the volume of air which ispumped at full capacity, then the controllever I50 is. set to position the follower. rollers 52 and II? on their respective cams and H5, so that the unloading valves 51 and 82 are positively held open until the pistons have completed about twothirds of their compression strokes.

While the. unloading valves 51 and 82 are open during the compression strokes in their respective cylinders II and I2, no airis compressed, but is discharged at approximately inlet pressure through said valves and into the inlet manifolds and pipes. The compression strokes in the cylinders II and I2 are thereby rendered ineffective for the portions thereof .during' which said unloading valves 51 and 82 are open. The effective portions of the compression strokes do not begin until these unloading valves 51 and, 32 are closed.

During the suction strokes, the air which has been compressed in the clearance spaces during the previous compression strokes, is expanded against the pistons, so that the work of compressing this air is not lost but returned to the pistons. When this air has been expanded to a pressure slightly below that of the air in the inlet pipe, the corresponding inlet valves 42 and 50 are automatically opened against their spring means by the differences in pressure on opposite sides of said valves. The unloading valves 51 and 82 are not opened until after these inlet valves 42 and 50 are open, so that these unloading valves do not interrupt the expansion of the clearance air against the pistons. These unloading valves 51 and 82 are desirably positively opened by the mechanical device shown, but as far as certain aspects of the invention are concerned, these valves may be initially opened automatically by the difierences in pressures on opposite sides of said valves as in the case of the inlet valves 42 and 50. The mechanical means will thenoper-ate only to positively maintain the unloading valves 57 and 82 open until their corresponding pistons have reached the desired points in their com pression strokes.

The eifective displacement of the two cylinders II and I2 will be simultaneously adjusted proportionately by the adjusting operations described, so that their relative displacement-s will be maintained substantially constant, irrespective of the setting of the control handle I50. Therefore, as long as the compressor is working against the final pressure for which its cylinders were designed, the ratio of compression in each cylinder remains substantially constant, and the ratios of compression of the two cylinders will be substantially equal, thereby assuring substantial equalization of work and heat generation in the two cylinders II and I2 for all settings of the control handle I50.

When the control handle I50 is set to position the rollers 92 and I IT in cam follower relationship with respect to the larger cylindrical end sections of their respective earns 90 and H5, as shown in Fig. 9, the unloading valves 5? and 82 will be maintained continuously open, and the compressor will be operating at Zero capacity.

It will be understood that since the air enters the low pressure cylinder from the atmosphere, and the air enters the high pressure cylinder from the intercooler the air entering both cylinders is relatively cool. Under all conditions ex cept when the compressor is working at full capacity some of the air taken into the cylinders on the suction stroke of the pistons is expelled therefrom on the compression strokes of the pistons. Thu-s there is produced a circulation of relatively cool air through the cylinders, which serves to cool them internally and effectively.

It may be desirable to maintain a substantially constant predetermined pressure in a receiver. To this end, an automatic control may be provided which is settable to the pressure required. This arrangement includes a pipe I66, Fig. 15, through which compressed air from the receiver tank 53 passes into a cylinder Ififia. This cylinder IGBa has therein a piston I61 which is urged towards the right by a spring I60. As the pressure increases in the receiver 53 the piston IE1 is forced towards the left in the cylinder I660. until it balances the pressure of the spring I68. A rod I69 connected to the piston I61 and to a lever arm I54 shifts the cam rollers 92 and Ill to reduce the effective displacement of the compressor until when the pressure reaches the maximum desired, no air is delivered. The constant at which the pressure is to be maintained may be varied by regulating the pressure of the spring I 68. This may be accomplished by a cap IBGb threaded on the end of the cylinder ISSa and engaging one end of the spring I68.

Although the invention is shown applied to a compressor of the multi-stage type, as far as certain aspects of the invention are concerned, this may be applied to a single-stage compressor.

Also, as far as certain aspects of the invention are concerned, instead of employing an unloading valve separate from the inlet valve, the inlet valve may be employed as an unloading valve,

opening by suction and held open mechanically substantially as described in connection with the unloading valves 51 and 92, or the inlet valve shown may be simply omitted. The unloading valve can act as an automatic inlet valve especially if its spring it not too stiff so that the inlet valve shown is really not necessary though perhaps desirable.

Moreover, as far as certain aspects of the invention are concerned, instead of varying the two effective displacements simultaneously and proportionally, these may be varied separately independently of each other, as by providing a separate control handle for each of the rollers 92 and i I? instead of the single handle shown in Fig. 5.

In Fig. 15, the invention is diagrammatically shown applied to a two-stage compressor with means to prevent warm air rejected through the unloadin valve 82 of the high pressure cylinder I2 from being again drawn into this cylinder before it is cooled in the intercooler I3. A check valve I64 permits air to flow from the in tercooler I3 only towards the high pressure cylinder I2. Warm air expelled through the unloading valves 82 of the high pressure cylinder I2 is caused to flow through check valve I65 into the hot end of the intercooler I3. In the intercooler I3, the air is reduced approximatelyto the intake temperature at the inlet of the low pressure cylinder II. Only cool air from the cool end of the intercooler I3 can enter the high pressure cylinder I2. 7

In Fig. 16 is shown a multi-cylinder two-stage compressor I0 provided with a single intercooler I75. The outlet pipes MB of the two low pressure cylinders II merge into a single pipe I" leading to the inlet of the intercooler I15. The outlet of the intercooler I15 has two parallel branch connections I18 provided with respective check valves I64, and leading to the inlets of the high pressure cylinders I2 respectively. The discharge sides of these high pressure cylinders I2 connect through pipes I into a common outlet I8I. The rejected air discharged through the unloading valves 82 of the high pressure cylinders I2 is returned through the check valves I65 and back into the intercooler I15, in the manner already described in connection with the arrangement of Fig. 15.

In Fig. 17 is shown a multi-cylinder two-stage compressor I0 similar to those shown in Fig. 16, the only differences being that there are two intercoolers I85, one for each compressor or, in other words, one for each set of cylinders.

In Fig. 18 is shown diagrammatically the present invention applied to a double-acting compressor I90. This compressor I is shown comprising a cylinder I9I having a piston therein operated from a crank shaft I93, through a crosshead I94, 9. connecting rod I between one side of said cross-head and a crank I96 on said crank shaft, and a piston rod I91 between the other side of said cross-head and said piston. Heads or water jackets I98 are provided at each end of the cylinder I9I and inlet valves 200 and discharge valves 20I. Each of the inlet ports for these inlet valves 200 connect into a chamber 202 having a filter 203 on its intake side. The outlet ports controlled by the discharge valves 20I connect into a common outlet 20 in the usual manner.

For varying the efiective displacement of the compressor I90 or in other words, the effective stroke thereof there are provided two unloading valves 205 one at each working end of the cylinder I9I, each valve operating in a port communicating with the inlet of the cylinder through the inlet chamber 202. Eachunloading valve 205 may be of the type similar to that shown in connection with the unloading valve 5'I of Figs. 1-14, but is operated from a bell crank 206 pivoted at 201, and having one arm 208 engaging the free end of the stem 2I0 to valve 205 to open the latter against the action of a spring, not shown. Each bell-crank 206 has another arm 2 carrying a roller 2I2 in follower engagement with a cam 2I3. The cam 2I3 shaped like the of shaft-like construction and designed to open positively the escape valves 205 atselected phases with respect to the corresponding strokes, and maintain them open for selected periods during their corresponding compression strokes according to the setting offthe cam 2|3. This cam 2H3 is not stationary as the cam 90 but mounted for axial adjustin movement, and when axially moved,-itjwill change the phases during which the unloading valves 205 are opened and closed so that the effective compression strokes of the piston E92 are changed, while maintaining said effective strokes on opposite sides of said piston substantially equal. It will be understoodtthat in this form of theinvention a single cam I is used to operate two unloading valves alternately at 180 intervals of rotation.

I have described what I believe to be the best embodiments of my invention. I do not wish, however, to be confined to the embodiments shown, but what I desire to cover by Letters'Patentis set forthin the appended claims.

, WhatIclaim is: i

1. A ,multi-stage compressor comprising at least two cylinder parts, a piston reciprocable in each of said cylinder parts, and means for selectively varying the effective volumetric displacement of each of said cylinderparts, comprising an unloading valve in each of said parts, adapted when open to prevent compression in the corre sponding cylinder part, mechanical means free from electric or fluid operation, for positively maintaining said valve open during aselec'ted portion of the compression stroke of the corresponding piston, and means for varying the phase at which each of said Valves is opened with respect to the stroke cycle of its corresponding piston, said means for changing the effective volumetric displacements of the cylinder parts comprising a plurality of cams corresponding to the compression cylinders in the i compressor, means for rotating said cams at predetermined relative angular rates, each of said cams being in the form of a shaft having a valve opening projectionprogressively changing lengthwise of said cam, a follower roller in engagement with each of said cams, a mechanical transmission free from mechanical or fluid operation between each of'said rollers and a corresponding unloading valve for maintaining said valve openduring a selected part of the compression stroke of the corresponding piston, and means for moving all of said followers in unison along their corresponding cams for simultaneously varying the phase relationship between the operatingjsections of said cams and the stroke cycles of the corresponding pistons.

2. A rnulti-stage compressor comprising two cylinders disposed alongside of each other, a piston reciprocable in each of said cylinders, a common crankcase for said cylinders, a crank shaft in said crankcase for operating said pistons, and means for selectively varying the effective volumetric displacement of each of said cylinders, comprising an unloading valve at the working end of each cylinder adapted when open to prevent the pressure from building up in said working end, said unloading valves being disposed on opposite sides of the common line of the two cylinders, a pair of parallel cams journalled for rotation in said crankcase and disposed on opposite sides of said crank shaft, each of said cams being in the form of a shaft having a valve openingconformation progressively changing lengthwise or said cams, means for driving said came from said crank shaft, a follower in engagement with each of said cams a transmission between each of said followerstand the corresponding unloading valve on the same side of the common center line of the two cylinders, for maintaining said valve open duringa selected part of the compression stroke of the corresponding piston, and means for moving saidfollowersalong their corresponding cams for varying the phase relationship between theoperative sections of said cams and the stroke cycles of their corresponding pistons. i i

3th multi-stage compressor as described claim 2, in which thevalve opening conformations on said camsextend apart, whereby saidcrankshaft mayberotated in either directicn without affecting th effective displacement of the cylinders. 4. A' compressor as described-in claim 2, including a control member; and means operable in response to said control member for moving cams. i i

5., A multi-stage compressor, comprising at least twocylinder parts, a piston reciprocable in said followers in unison along their respective each of said cylinder parts, a controlmember,

and means operable in accordance with the-setting of said control member for varying "the effectivevolumetric displacement of each of said cylinder parts, said means being operable to the crank shaft in either direction Without vary ing the effective displacement of said cylinder parts for a particulansetting of said control member. i i

"7. A 'compressorjcomprising a, cylinder, a piston reciprocable therein,yan inlet" port on one side of said cylinder at its working end, an inlet valve for said port, andmeans for selectively varying the effective volumetric displacement of said cylinder, and comprising an unloading port at the'wo rki'ng end of said cylinderya passageway around said cylinder establishingcommunication between said ports, an unloading valve in said unloading port adapted when open to prevent the pressure from building up in said working end, mechanical means for positively maintaining said unloading valve open during the forepart of the compression stroke, and means for selectively varying the opening and closing phases of said unloading valve relative to the stroke cycle of said piston.

8. A compressor comprising a cylinder, a piston reciprocable therein, an inlet port on one side of said cylinder at its working end, an inlet valve for said port, and means for selectively varying the eifective volumetric displacement of said when opento prevent the pressure from building up'in said working end, means for maintaining said unloading valve open during the iorepart of the compression stroke, and means for selectively varying the closing phase of said unloading valve relative to the compression stroke of said piston.

9. A compressor comprising a cylinder afiording a clearance space, a piston reciprocable therein, an inlet valve at "the closed end of said cylinder operable in accordance with the difference in pressures on opposite sides thereof, and means for varying the effective volumetric displacement of said compressor, comprising an unloading valve at the closed end of said cylinder separate, from said inlet valve and adapted when open to prevent the compression of air in the cylinder, said valves being disposed in respective ports communicating with each other, means whereby said unloading valve is opened during the suction stroke but not before said inlet valve has been opened, mechanical means free from fluid or electric operation and actuated in synchronisrn with the reciprocation of said piston for positively maintaining said unloading valve;

open during the forepart of the compression stroke, said latter means being mechanically releasable at a selected phase relative to the compression stroke cycle of the piston to permit closing of said unloading valve and the compression and delivery of compressed air during the remainder of the compression stroke, and means for varying the phase at which said last mentio'nedvalve maintaining means is released, to

vary the effective volumetric displacement of said compressor.

10. A compressor as described in claim 9, in

which the position of opening of the unloading valve with reference to the beginning of the suction stroke is substantially the same as the.

position of the closing of said unloading valve with reference to the end of the compression stroke regardless of operation of said phase varying means.

11. A multi-stage compressor comprising at least two cylinder parts, a piston reciprocable in each of said cylinder parts, and means for varying the efiective volumetric displacement of each of said cylinder parts, comprising an unloading valve in each of said parts, adapted when open to prevent compression in the corresponding cylinder part, a plurality of cams corresponding to the number of cylinder parts in the compressor, a mechanical transmission free from electric or fluid operation between each of said cams and a corresponding unloading valve for mainpressor, including an unloading valve at the closed end of said cylinder, means for opening said valve during the suction stroke and, closing said valve during the compression stroke, the phase in the suction stroke when said valve opens as measured from the end of the suction stroke corresponding to the phase in the compression stroke when said valve closes as measured from the beginning of the compression stroke, and means for varying the phase at which said unloading valve is opened and closed, while maintaining correspondence between the opening phase of the valve during the suction stroke and closing of the valve during the compression stroke.

13. A multi-stage compressor comprising at least two cylinders, a crankcase, a crankshaft in said crankcase, a piston reciprocable in each of said cylinders, and means for selectively varying the-effective volumetric displacement of each of said cylinders comprising an unloading valve in each of said cylinders, adapted when open to prevent compression in the corresponding cylinder, a pluralityof cams corresponding to the number of cylinders in the compressor and mounted in said crankcase, means for driving said cams from said crankshaft, a mechanical transmission free from mechanical or fluid oper ation between each of said cams and acorrespending unloading valve for maintaining said valve open during a selected part of the compression stroke of the corresponding piston, and means for varying the phase relationship between each cam and the stroke cycle of the-corresponding piston.

, HARVEY W. BELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,598,637 Bayles Sept. 7, 1926 2,032,429 Metzgar Mar. 3, 1936 2,167,369 Paullin, Jr July 25, 1939 2,176,716 Jump Oct. 17, 1939 2,302,847 Ferguson Nov. 24, 1942 2,339,191 Raymond Jan. 11, 1944 

